1. Field of the Invention
The present invention relates to a piezoelectric actuator device that is used, for example, in a wire-dot printing machine.
2. Description of the Related Art
A wire-dot printing machine comprises a plurality of printing elements each of which includes a printing wire for striking the paper to be printed. With the increased printing speed in the wire-dot printing machine, a piezoelectric actuator device comprising a piezoelectric assembly is often used in the printing element to move the printing wire in response to a given signal. The movement of the piezoelectric assembly is very small and a movement magnifying mechanism is provided in the printing element for magnifying the movement of the piezoelectric assembly and for transferring the magnified movement to the printing wire.
The movement magnifying mechanism includes a rigid member carrying the printing wire, a first spring attached to the piezoelectric assembly, and a second spring connecting the rigid member to the support base. The rigid member of the movement magnifying mechanism is thus pivotally supported to the base of the printing element by the second spring and moved by the piezoelectric assembly via the first spring.
The piezoelectric assembly is instantaneously activated to move the printing wire toward the paper to print a dot on the paper and then deactivated to return the printing wire. This action causes the rigid member of the movement magnifying mechanism to vibrate after the piezoelectric body is deactivated, and this vibration causes the printing wire to rebound toward the paper. If the amount of the rebound of the printing wire is large, the printing wire may reach the paper even though the piezoelectric assembly is not activate and make a ghost on the paper. If the piezoelectric assembly is next activated while the rigid member is vibrating and when it is returning to the original position, the desired movement of the rigid member toward the paper may not be smoothly accomplished. Also, the vibration of the rigid member of one of the printing elements is transferred to the rigid member of another printing element.